The present invention relates to an inflating-type safety system for a motor vehicle, more specifically to a hybrid inflator capable of inflating an air bag reliably and rapidly, and to an air bag system using the hybrid inflator.
1. Prior Art
With the development of an inflator for an inflating-type safety system of motor vehicles, a hybrid inflator using both a pressurized gas and a solid gas generating agent has been attracting attention. A main design requirement for a hybrid inflator is that the inflator inflates an air bag to a predetermined amount in a predetermined time so that the air bag is effectively activated. Various proposals concerning a structure to meet the requirement have heretofore been made (for example, as referred in JP-A 8-2824 27). Since such a hybrid inflator is manufactured to be installed in a motor vehicle, the weight and dimensions of the inflator, which have influence upon the weight of the motor vehicle, constitute an important design requirement therefor. And it is required to reduce the weight and number of parts while maintaining function as the hybrid inflator.
2. Disclosure of the Invention
An object of the present invention is to provide a hybrid inflator in which a weight of the inflator can be reduced and manufacturing process can be simplified, and to provide an air bag system using such a hybrid inflator.
A hybrid inflator of the present invention can be applied to any of a single type hybrid inflator having a single gas generating chamber and a multistage inflating hybrid inflator having two (dual type) or more than three gas generating chambers.
The present invention provides, as one means for solving the above problem, a hybrid inflator for an inflating-type safety system of a vehicle provided with an air bag, which comprises an inflator housing, a gas generator provided in the inflator housing, and an ignition means chamber having an ignition means joined to the gas generator, wherein
the interior of the inflator housing is filled with a pressurized medium containing an inert gas,
the gas generator has an outer shell formed by a gas generator housing having a plurality of communication holes, the gas generator includes, in the gas generator housing, a gas generating chamber which accommodates a gas generating agent, the gas generating chamber and the inflator housing are in communication with each other through the communication holes,
each of the communication holes provided in the gas generator housing has such a size that combustion gas generate in the gas generating chamber can flow out therethrough but the gas generating agent can be prevented from leaking outside.
This hybrid inflator is of a single type having one gas generating chamber. It is possible to prevent the gas generating agent from leaking outside without using a leak-blocking screen by adjusting a size (hole diameter) of the plurality of the communication holes. Since the screen for covering the communication holes by which the inflator housing communicates with the gas generating chamber provided in the gas generator housing is not used, a weight of the hybrid inflator can be reduced by a weight of the screen. Further, since a mounting step of the screen is unnecessary, the number of manufacturing steps can be reduced, and the manufacturing step can be simplified.
Further, as another means for solving the above problem, the present invention provides a hybrid inflator for an inflating-type safety system for a vehicle provided with an air bag, which comprises an inflator housing, a gas generator provided in the inflator housing, and an ignition means chamber having ignition means connected to the gas generator, wherein
the gas generating agent can be prevented from leaking outside. pressurized medium containing an inert gas,
the gas generator has an outer shell formed by a gas generator housing having a plurality of first and second communication holes,
the gas generator housing includes, therein, first and second gas generating chambers each having a gas generating agent, the first gas generating chamber and the inflator housing are in communication with each other through the first communication holes, the second gas generating chamber and the inflator housing are in communication with each other through the second communication holes,
each of the first and/or second communication holes has such a size that combustion gas generated in the first and/or second gas generating chamber can flow out therethrough but the gas generating agent can be prevented from leaking outside.
In the present invention, the following three modes may be employed: (a) the plurality of the first communication holes are not covered by the screen, but the plurality of the second communication holes are covered by the screen, (b) the first communication holes are covered by the screen, but the second communication holes are not covered by the screen, and (c) both the first and second communication holes are not covered by the screen. Among these embodiments, (c) is most preferable.
This hybrid inflator is of a dual-type having two gas generating chambers. Like the above-described single type hybrid inflator, it is possible to prevent the gas generating agent from leaking outside by adjusting a size (hole diameter) of the first and second communication holes without using a screen. Since the screen for covering the plurality of the communication holes by which the inflator housing communicates with the gas generating chambers provided in the gas generator housing is not used, a weight of the hybrid inflator can be reduced by a weight of the screen. Further, since a mounting step of the screen can be omitted, the number of manufacturing steps can be reduced, and thereby, the manufacturing step can be simplified. In a conventional dual-type hybrid inflator, a screen is mounted on each of the first and second communication holes. Since the screens are not used, the number of parts can be reduced by two, and since the mounting step of the two screens can be omitted, effects of reducing a weight and simplifying manufacturing steps are extremely great.
In the hybrid inflator of the present invention, the plurality of the communication holes or the plurality of the first and second communication holes provided in the gas generator housing can have the same hole diameters. By setting the hole diameters of the communication holes to the same, it becomes easy to control the amount of outflow and the outflow state of combustion gas generated by burning the gas generating agent, and additionally, manufacture of the gas generator housing can be facilitated.
In the hybrid inflator of the present invention, plurality of the communication holes or the plurality of the first and second communication holes provided in the gas generator housing may have hole diameters in a range of 0.5 to 3 mm, more preferably in a range of 1.0 to 2.0 mm. By setting the hole diameter of each of the plurality of the communication holes or the plurality of the first and second communication holes in the predetermined range, the amount of outflow and the outflow-state of a combustion gas generated by combustion of the gas generating agent can be controlled easily.
And, in the hybrid inflator of the present invention, the total number of the communication holes or the first and second communication holes provided in the gas generator housing may be 100 to 600, more preferably 200 to 500. By setting the total number of the communication holes or the first and second communication holes in a predetermined range, the amount of outflow and the outflow-state of a combustion gas generated by combustion of the gas generating agent can be controlled easily.
And, in the dual-type hybrid inflator of the present invention, the total number of the first communication holes may be 50 to 300, more preferably 100 to 250, and the total number of the second communication holes may be 50 to 300, more preferably 100 to 250. By setting the total number of the first and second communication holes in a predetermined range, the amount of outflow and the outflow-state of a combustion gas generated by combustion of the gas generating agent can be controlled easily.
And, in the hybrid inflator of the present invention, the total open area of the communication holes or the first and second communication holes provided in the gas generator housing may be 100 to 600 mm2, more preferable 200 to 500 mm2. By setting the total open area of the communication holes or the first and second communication holes in the predetermine range, the amount of outflow and the outflow-state of a combustion gas generated by combustion of the gas generating agent can be controlled easily.
And, in the hybrid inflator of the present invention, the plurality of the communication holes or the plurality of the first and second communication holes provided in the gas generator housing may be arranged in a plurality of lines in the longitudinal direction of the gas generator housing as well as in a plurality of lines in the outer peripheral direction. By arranging the communication holes in plurality of the lines, requirements concerning the hole diameter, the total number and the opening area of the communication holes can be controlled easily, and thereby, the hybrid inflator which fulfills the requirements can be produced efficiently.
Further, as another means for solving the above problem, the present invention provides a hybrid inflator for an inflating-type safety system of a vehicle provided with an air bag, which comprises an inflator housing, a gas generator provided in the inflator housing, and an ignition means chamber having ignition means connected to the gas generator, wherein
the interior of the inflator housing is filled with a pressurized medium containing an inert gas,
the gas generator has an outer shell formed by a gas generator housing having a plurality of first and second communication holes,
the gas generator housing includes, therein, first and second gas generating chambers each having a gas generating agent, a first ignition means. chamber having first ignition means is connected to a first gas generating chamber, a second ignition means chamber having second ignition means is connected to a second gas generating chamber, the first gas generating chamber and the inflator housing are in communication with each other through a plurality of the first communication holes, the second gas generating chamber and the inflator housing are in communication with each other through a plurality of the second communication holes,
each of the first and/or second communication holes has such a size that combustion gas generated in the first and second gas generating chambers can flow out therethrough but the gas generating agent can be prevented from leaking outside, the second communication holes are disposed:at a distance from the second ignition means in the widthwise direction and/or the longitudinal direction of the inflator housing.
In this invention, the expression xe2x80x9cthe second communication holes are disposed at a distance from the second ignition means in the widthwise direction and/or the longitudinal direction of the inflator housingxe2x80x9d includes three states from the second ignition means, i.e. a state in which the second communication holes are disposed at a distance in the widthwise direction, a state in which the second communication holes are disposed at a distance in the longitudinal direction, and a state in which the second communication holes are disposed at a distance in both widthwise and longitudinal directions. The widthwise direction of the inflator housing means a direction/on toward the side-walls of the inflator housing with respect to the center axis of the inflator housing in its longitudinal direction.
When the second communication holes are disposed at a distance in the widthwise direction of the inflator housing, it is preferable that all of the second communication holes are disposed in different directions from the second ignition means in the widthwise direction of the inflator housing. When the communication holes are disposed in different directions in the widthwise direction of the inflator housing, it is preferable that all of the second communication holes are directed to a direction different from the second ignition means through 90xc2x0 or greater in the widthwise direction.
In the hybrid inflator of the present invention, like the above-described single type hybrid inflator, it is possible to prevent the gas generating agent from leaking outside by adjusting a size (hole diameter) of each of the first and/or second communication holes without using a leak-blocking screen. And, since such a screen can be omitted, the weight of the inflator can be reduced, the manufacturing step can be simplified, and leaking of the gas generating agent can be prevented. With respect to relation between the first and second communication holes and the screen, the above-described three modes, (a)-(c), can be employed, and the mode (c) if most preferable.
And, in the hybrid inflator of the present invention when the second communication holes and the second ignition means are disposed close to each other (i.e., when they are disposed such that the widthwise direction of the inflator housing is the same direction as an example thereof shown in FIG. 3, all the gas generating agent can be burned smoothly and uniformly by employing the above-described arrangement. Without the above arrangement, in general, the gas generating agent near the second communication holes is burned smoothly, but there is an adverse possibility that gas generating agent away from the second communication holes is not burned smoothly.
The gas generating agent used in the hybrid inflator of the present invention is not specially limited, and one example thereof is shown below. In the hybrid inflator of the present invention, as shown in 1) and 2) below, a gas generating agent accommodated in one gas generating chamber for a single type hybrid inflator, or a first gas generating,agent accommodated in the first gas generating chamber and a second gas generating agent accommodated in the second gas generating chamber for a dual type hybrid inflator can be determined based on a relation with composition of pressurized medium charged in the inflator housing.
1) the pressurized medium including oxygen:
When the pressurized medium consists of oxygen and an inert gas such as argon, helium (nitrogen is also included in the inert gas in the present invention), etc., the oxygen works to convert carbon monoxide and hydrogen generated due to the combustion of a gas generating agent as gas generating means into carbon dioxide and vapor, while the inert gas works to promote the thermal expansion of the pressurized medium. It is preferable to contain helium in the pressurized medium since the leakage of the pressurized medium can be detected easily, for the purpose of preventing distribution of the imperfect products. Concrete compositions of the pressurized medium including oxygen are determined in accordance with gas generating agent to be used and a kind thereof, and the content of oxygen is preferably about 8 to 30 mol %. A charging pressure of the pressurized medium (=pressure in the inflator housing) is preferably 10,000 to 70,000 kPa and more preferably, 30,000 to 60,000 kPa.
As the gas generating agent in the single type hybrid inflator and the dual type hybrid inflator, a gun propellant can be used for example. As the gun propellant, a single-base gun propellant, a double-base gun propellant and a triple-base gun propellant can be used. In addition to them, it is possible to use a gun propellant obtained by mixing a secondary explosive, a bonding agent, a plasticizer and a stabilizer and the like, and molding the resultant mixture to a desired shape.
The secondary explosive can include hexahydrotrinitrotriazine (RDX), cyclotetramethylene tetranitramine (HMX), pentaerithritol tetranitrate (PETN) an triaminoguanidine nitrate (TAGN). For example, when a gas generating agent using RDX as a secondary explosive is burned in an oxygen-absent atmosphere under a pressure of 20,670 kpa and at a combustion temperature of 3348 K, a formed gas in a combustion gas comprises 33 mol % of nitrogen, 25 mol % of carbon monoxide, 23 mol % of vapor, 8 mol % of carbon dioxide and other gas components.
The bonding agent can include cellulose acetate, cellulose acetate butylate, cellulose acetate propiolate, ethyl cellulose, polyvinyl acetate, azide polymer, polybutadiene, polybutadiene hydride and polyurethane; the platicizer can include trimethylolethane trinitrate, butantriol trinitrate, nitroglycerine, bis (2,2-dintropropyl) acetal/formal, glycidyl azide and acetyltriethl citrate and the like; and the stabilizer can include ethlcentralite, diphenylamine and loesosinol.
A preferable ratio of the secondary explosive to the bonding agent, plasticizer and stabilizer is about 50 to 90 wt. % of secondary explosive to about 10 to 50 wt. % of bonding agent, plasticizer and stabilizer in all.
It is difficult in some cases to burn the gas generating agent of the above-described composition under normal pressure. However, in the hybrid inflator according to the present invention, since the interior thereof is maintained at a high pressure in advance, the gas generating agents can be burned stably and smoothly.
2) the pressurized medium not including oxygen:
When the pressurized medium consists of substantially an inert gas such as argon, helium (nitrogen is also included in the inert gas in the present invention), etc., the inert gas works to promote the thermal expansion of the pressurized medium. It is preferable to contain helium in the pressurized medium since the leakage of the pressurized medium can be detected easily for the purpose of preventing distribution of the imperfect products. A charging pressure of the pressurized medium is preferably 10,000 to 70,000 kPa and more preferably, 30,000 to 60,000 kPa.
As the gas generating agent accommodated in the single type hybrid inflator and the dual type hybrid inflator, it is possible to use a material including fuel and oxidizer, or fuel, oxidizer and slug-forming agent which are mixed together with bonding agent if necessary and formed into a desired shape. If such a gas generating agent is used, a gas generated by its combustion can be supplied together with the pressurized medium for developing the air bag. Especially when the gas generating agent including the slug-forming agent is used, the amount of mist discharged from the inflator can be, reduced much.
Preferably, the fuel can be one or two or more materials selected from a group consisting guanidinie derivative such as nitroguanidine (NQ), guanidine nitrite (GN), guanidine carbonate, amino nitroguanicine, amino guanidine nitrite, amino guanidine carbonate, diamino guanidine nitrite, diamino guanidine carbonate, and triamino guanidine nitrite. Further as the fuel, one or two or more materials selected from a group comprising tetrazole and tetrazole derivative can be used
As oxidizer, one or two or more materials selected from a group comprising strontium nitrate, potassium nitrate, ammoniumnitrate, potassium perchlorate, copper oxide, ferrous oxide, basic copper nitrate can be used. Preferable composition amount of oxidizer is 10 to 80 parts by weight, and more preferably, 20 to 50 parts by weight with respect to 100 parts by weight of fuel.
Preferably, the slug-forming agent can be one or two or more materials selected from a group consisting of acid clay, talc, bentonite, diatomaceous earth, kaolin, silica, alumina, sodium silicate, silicon nitride, silicon carbide, hydrotalsite, and a mixture thereof. Preferable composition amount of slug-forming agent is 0 to 50 parts by weight, and more preferably, 1 to 10 parts by weight with respect to 100 parts by weight of fuel.
Preferably, the bonding agent can be one or two or more materials selected from a group consisting of sodium salt of sodium carboxymethylcellulose, hydroxyethyl cellulose, starch, polyvinyl alcohol, guar gum, microcrystal cellulose, polyacrylamide and calcium stearate. Preferable composition amount of the bonding agent is 0 to 30 parts by weight, and more preferably, 3 to 10 parts by weight with respect to 100 parts by weight of fuel.
When the pressurized medium and the gas generating agent having the above-described compositions are used, it is preferable that a molar ratio (A/B) between an amount (A mol) of the pressurized medium and an amount (B mol) of a gas generated due to combustion of the gals generating agent is adjusted to 8/2 to 1/9, and more preferably 8/2 to 3/7.
As described above, the charging amount of the pressurized medium can be reduced by adjusting the molar ratio between the amount of pressurized medium charged in the hybrid inflator and the amount of a gas generated by combustion of the gas generating agent. Therefore, even when the volume of the inflator housing is reduced (i.e., even when the length and/or width (diameter) of the housing is reduced), it is possible to maintain the pressure at the same level as that before the volume is reduced, without enhancing the charging pressure (internal pressure of the housing) of the pressurized medium. In the hybrid inflator of the present invention, the weight ratio (a/b) of the weight (a) of the pressurized medium to the weight (b) of the gas generating agent is preferably 0.1 to 7, and more preferably 1 to 7.
In the above hybrid inflator, it is preferable that a pressure index determined by the following formula: rb=xcex1Pn (wherein, rb: burning rate, xcex1: coefficient, P: pressure, n: pressure index), at the combustion of the gas generating agent, is smaller than 0.8. The pressure index (n) is preferably 0.2 to 0.7, and more preferably, 0.4 to 0.6.
The pressure index (n) is obtained from two formulas, i.e., rb1=xcex1P1n and rb2=xcex1p2n, after a burning rate rb1 is measured in a pump having a pressure P1 (70 kg/cm2), and a burning rate rb2 is measured in a pump having a pressure P2 (100 kg/cm2).
When the pressure index (n) is set to smaller than 0.8 in this manner, the burning rate at the initial state of the combustion of the gas generating agent is restrained from increasing abruptly, whereby, increase of the pressure inside the housing is small. Accordingly, a sufficient pressure resistance of the housing can be maintained even if the thickness of the housing is reduced. Further, since the increase in the internal pressure of the housing is small (i.e. a variation in the internal pressure is small), the gas generating agent is burned stably so that all the gas generating agent is burned completely.
In the hybrid inflator of the present invention, as a relation between the pressurized medium and the gas generating agent, the above-described combinations 1) and 2) may be employed, and the combination 2) is more preferable.
Further, the present invention provides an air bag system comprising activation-signal outputting means including an impact sensor and a control unit, and. a module which accommodates the above-described hybrid inflator and air bag, wherein the inflating speed of the air bag, can be adjusted.
In the present invention, the term xe2x80x9cgas generatorxe2x80x9d is the one having a gas generating performance to generate a high temperature combustion gas due to combustion of the gas generating means (gas generating agent) in the gas generator housing (gas generating chamber), thereby allowing the high temperature combustion gas to flow into the inflator housing. The hybrid inflator includes the gas generator in its inflator housing, and the term xe2x80x9cinflatorxe2x80x9d is the one having a performance to flow outside, the pressurized medium existing inside of the inflator housing as well as outside of the gas generator to inflate an object to be inflated such as an air bag by flowing a high temperature combustion gas from the gas generator into the housing. The term xe2x80x9chybridxe2x80x9d means a combination of the high temperature combustion gas generated by combustion of the gas generating agent and the pressurized medium.
In the hybrid inflator of the present invention, since the leak-blocking screen, for covering the communication holes by which the inflator housing communicates with the gas generating chamber provided in the gas generator housing, is not used, the number of parts and manufacturing steps can be reduced, and thereby the cost can be effectively reduced because of weight-reduction of the hybrid inflator and the facilitated manufacturing process.